Such foundation construction devices for making trenches are lowered on a carrier device whilst being suspended thereon. Through rotating movements of cutting wheels, grabs or scoops the soil is removed in a generally rectangular cross-sectional surface so that a trench filled with suspension is produced in the soil. In order to make a trench wall this procedure can be repeated in a horizontally spaced position.
The soil can consist of different sand layers, stone layers, rock and cavities. This can give rise to undesirable deviations of the foundation construction devices. Even minor changes of direction of the foundation construction device may, in greater trench depths, lead to considerable gaps in the trench wall.
From DE-C-36 15 068 a cable-guided trench wall grab is known, on the grab frame of which a guide frame is longitudinally movable on the outside. The guide frame is lowered with the grab into the trench where it is braced against the walls of the trench by means of extendable spacer plates. In the guide frame the grab frame can be guided in the vertical direction during the movements required to strip the soil. In doing so the bracing of the guide frame in the trench is controlled such that the grab axis is always located in the centre of the trench. To this end the spacer plates are extended on either side of the grab axis equidistant thereto either by means of levers actuated through cylinder-piston units or directly by cylinder-piston units that can be controlled separately for each spacer plate. By using displacement measuring devices that indicate the position of the cylinder-piston units and an inclination measuring instrument that indicates the position of the grab frame to the vertical line a position of the grab in the trench can be controlled to a certain degree.
From the disclosed document EP-A-0 518 298 a trench wall cutter and a cutting method for making trench walls with random angles of inclination are known. For this purpose control flaps are arranged on a vertically movable cutting frame, which, by projecting as far as beyond the outer border of the cutting frame, can be driven through hydraulic cylinders. In the cutting frame an inclinometer is arranged for directional correction. The hydraulic cylinders can in addition have a displacement pick-up und a pressure switch for the position of the control flaps. The control flaps can be prestressed against the trench wall either at the lower end or at the upper end thereof, whereby a torque acting in a predetermined direction on the cutting frame is generated.